Estuaries in the Gulf of America (Gulf) are experiencing increased temperatures, flood-producing storms, and more extreme weather events. As the climate continues to change, it’s important for fisheries managers to understand how environmental conditions influence localized fish and invertebrate populations. Fisheries-independent monitoring data provide valuable insight into juvenile recruitment dynamics, enabling examination of these patterns relative to changing habitat conditions. 

The Mississippi Sound is an estuary complex naturally influenced by six tributaries, but recent rainfall patterns and a freshwater diversion structure pose considerable threats. Periodic openings of the Bonnet Carré Spillway cause rapid freshwater influxes, altering salinity and exerting significant impacts on resident species. In recent years, the frequency and duration of Spillway openings have increased, with events in 2011 and 2019 resulting in federally declared fisheries disasters.

We evaluated relationships between hydrological variability and juvenile recruitment of eight ecologically and economically important species: brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), blue crab (Callinectes spp.), Atlantic Croaker (Micropogonias undulatus), Sand Seatrout (Cynoscion arenarius), Spotted Seatrout (Cynoscion nebulosus), Spot (Leiostomus xanthurus), and Gulf Menhaden (Brevoortia patronus). A 15-year (2009–2023) fishery-independent trawl survey dataset analyzed using generalized additive models with negative binomial error structures assessed the influence of temperature, salinity, river discharge, and Spillway discharge on juvenile abundance. All species exhibited shifts in peak recruitment associated with hydrological variability and Spillway influence, although the direction and magnitude of effects varied among species. In general, freshwater discharge events had stronger effect than changes in temperature or salinity.

Discharge effects exhibited strong spatial structure, varying with distance from the freshwater input. Species exhibiting negative responses to river discharge (e.g., brown shrimp and Sand Seatrout) also responded negatively to Spillway diversion, whereas species responding positively to river discharge benefited from moderate Spillway flow. However, extreme or prolonged Spillway openings led to substantial declines, with blue crab exhibiting the only positive response. These findings suggest that diversion strategies mimicking natural discharge variability — favoring a series of shorter, moderate pulses over prolonged, high-magnitude releases — may reduce ecological impacts on nursery habitats while still meeting flood control objectives.